Strain Differences in the Facilitatory Action of Angiotensin on Noradrenergic Transmission in the Rat Mesentery

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Abstract
The isolated perfused rat mesenteric vasculature preparation was used to assess the contributions of presynaptic as well as postsynaptic mechanisms in the adrenergic potentiating action of angiotensin II in different rat strains. Angiotensin II (3 ng/ml; 2.5×10 12M) potentiated vasoconstrictor responses to periarterial nerve stimulation in mesentery obtained from Sprague-Dawley (SD) rats by 102.5±6.2% (p < .05) but did not significantly affect responses in mesentery from Wistar (W) rats. Responses to nerve stimulation were increased in W rats by 22.6±12.9% (p < .05) at higher concentrations of angiotensin II (10 ng/ml; 8.5×10-12M). The facilitatory actions of angiotensin II on nerve stimulation responses were antagonized by saralasin. Angiotensin II (2.5 or 8.5×10 12M) had little or no effect on responses to norepinephrine in mesentery from either SD or W rats. Blockade of neuronal and extraneuronal uptake potentiated the effects of angiotensin II on the responses to nerve stimulation in mesentery from W rats but not in mesentery from SD rats. The data suggest that angiotensin II increases norepinephrine release during nerve stimulation in mesentery obtained from SD and W rats. However, due to differences in the ability of the two strains of rats to compensate for the effect through increased neurotransmitter reuptake, the net effect on nerve stimulation responses is a large increase (100–110%) in SD rats as opposed to only a slight increase (15–20%) in W rats.